Surface maintenance equipment is available in a wide variety of types and sizes. Some of such equipment is designed for indoor use while other is particularly adapted for use in caring for large outdoor areas such as parks, cemeteries, large lawns and parking lots. The present invention is generally of the latter type although it is suitable for use in other environments, e.g. clothing factories.
Surface maintenance equipment in the past has typically included a body portion which is supported on a plurality of wheels. Some of the wheels may be driven by a power source such as a gasoline engine or electric motor. The body portion will usually carry a hopper for containment of dirt and debris which has been picked up. In some instances the equipment may be articulated and include a cab portion and a trailer portion. The equipment will generally include a debris pickup housing which defines a zone from which the grass clippings, dirt and debris are lifted and deposited into the hopper. A rotatably driven cylindrical tool such as a brush or paddle structure may be disposed in the pickup housing to assist in lifting the grass clippings, dirt, and debris. A duct may provide communication between the debris pickup housing and the hopper. A pump or blower may vacuumize the debris pickup housing and the ducts to assist in lifting and transporting debris material. Surface maintenance equipment of course includes various controls such as steering mechanism, speed controls and the like. The general type of equipment contemplated in the present invention is illustrated in U.S. Pat. Nos. 3,837,038 (Kimzey) and 3,881,215 (Krier) which are assigned to the Tennant Company.
Surface maintenance equipment used in areas having lightweight debris such as grass clippings encounters some somewhat unique problems. In particular it has been found that grass clippings and the like may remain airborne in the hopper such that they accumulate on the surface of the filter which cleans the air being expelled to the atmosphere. It has been known in the past to vibrate a filter such as a panel or bag filter to displace accumulated dust and dirt particles. Such approach is not completely satisfactory when the accumulated debris is materials such as grass clippings or lint. In other words, such material is not easily dislodged from the filter and the filter becomes blinded, thus reducing the effectiveness of the vacuum system. The present invention overcomes such problems by provision of a secondary screening system which removes the grass clippings, lint, and the like prior to the air approaching the filter.